If you happen to have a persistently annoying insect pest in your garden, doing absolutely nothing about it may be the best form of managing its spread long term.
In due course, natural predators — ladybugs, lacewings, pirate bugs or parasitic wasps — are likely to find the offending pest and begin to feast upon it. Or, if the plant’s natural predators are only found in its land of origin, entomologists (insect experts) may decide to import those predators and, after instituting a breeding program, release huge numbers of them as a biological control tactic.
Typically, the imported insect predator is a parasitic wasp. Parasitic wasps are so tiny as to be virtually invisible. As many as 30 of them could stand together on the head of a pin. Parasitic wasps lay their eggs in the eggs, larvae (caterpillars), nymphs or adults of the insect pest. After the parasitic wasp larvae hatch, they cannibalize their egg, larval, nymph or adult insect pest hosts.
In 1988, the ash whitefly was a major pest in ash trees and other ornamental plants throughout Los Angeles. The whitefly infestation was so severe that it posed a health hazard since you could hardly breathe in some areas without inhaling whiteflies. A parasitic wasp from the Mediterranean habitat of the ash whitefly was imported and, after two years, had the ash whitefly under control.
In 1992, the giant whitefly, originating in Guadalajara, Mexico, appeared in San Diego and arrived in Los Angeles soon afterward.
The favorite plant host of this pest is hibiscus, but it is found on many other ornamental plants as well, including xylosma, citrus and philodendron.
The San Diego Zoo was concerned about the giant whitefly since hibiscus grown on site is fed to many of its animals, especially reptiles such as iguanas and giant tortoises. Parasitic wasps from Texas and Central America were subsequently introduced and helped control the giant whitefly at the zoo. Incidentally, if you decide to feed hibiscus to your reptile, make sure the plants used are pesticide-free.
And now this year, for the first time in more than two decades, I did not notice any giant whitefly on Valley hibiscus plants and thought that our whitefly travails were finally over.
Alas, such good fortune is not to be. Just when I thought we could at last breathe a sigh of relief regarding whiteflies, the Ficus whitefly has started to make its pestiferous presence felt. An email I received recently from a Valley Village correspondent, who wishes to remain anonymous, alerted me as to its arrival. I subsequently learned that it was first spotted in the Los Angeles area in 2012.
Keep in mind that a whitefly has no relationship to true flies. The whitefly, which is a type of scale, is in the same insect order (Hemiptera) as aphids, mealybugs and thrips. These insects, which are the most damaging to garden plants, are known among insect specialists as “true bugs.”
The adult stage of the whitefly has perfectly white wings and flits around but does not damage plants. Instead, a whitefly crawler hatches from an egg and strolls around a leaf until it finds a spot to which it, literally, becomes attached. In this, its nymph stage, it sucks sap from the leaf.
An infested Ficus tree may defoliate completely as the result of concerted sap sucking on the part of tens of thousands of whitefly nymphs. The weeping fig (Ficus benjamina) is more susceptible to whitefly depradations than any other Ficus species, although Indian laurel fig (Ficus nitida), the most popular tree used for hedging Los Angeles property lines, is also an attractive target.
The email I received was from a homeowner who had several dozen Indian laurel figs, 20 years old and 30 feet tall, that were under whitefly attack. Fortunately, the edible fig (Ficus carica) does not seem to be of interest to the Ficus whitefly.
And it also would appear that Ficus whitefly will not be as daunting a challenge to contain as the ash and giant whiteflies. Even a tree completely defoliated by Ficus whitefly, the first time around, will produce a new batch of leaves. However, if the tree goes untreated, the law of diminishing returns will establish itself and the tree will weaken progressively with each defoliation, when death could ultimately ensue.
Still, I never recall an ash tree or hibiscus dying from a whitefly infestation and, hopefully, Ficus trees will be similarly resilient. Moreover, ash and giant whiteflies were impervious to chemical applications while Ficus whitefly will succumb to them. There are chemicals that you apply to the soil (that soak into the roots) or spray on the bark that move through the tree systemically, deterring Ficus whitefly.
If you are averse to applying systemic chemicals, you can provide relief by spraying horticultural oil, Neem oil, or insecticidal soap on the foliage at regular intervals. Make sure to do this on both sides of the leaves. During peak infestation during the summer months, it will be necessary to spray every five days since that’s how long it takes for a whitefly to complete its life cycle from egg to adult.
Do not spray toxic chemicals on Ficus foliage to deter whitefly since these chemicals will also deter beneficial predators. Fortunately, local insects — including lady beetles, green lacewings and parasitic wasps — have been identified as predators that may prevent the Ficus whitefly from wreaking unrestrained havoc on our Ficus hedges.
Since the Ficus whitefly’s habitat is India, China and Burma, it is hoped that natural predators from that part of the world may also be imported to assist in its control.
Another way of combating whiteflies is with sticky traps. You can either purchase these at nurseries or make them yourself from poster board. Cut out 6-inch by 12-inch pieces and cover them with yellow paint. In a bowl, make a mixture out of one part petroleum jelly or mineral oil and one part liquid laundry detergent and slather it onto your sticky traps once the yellow paint has dried. Make holes in the strips and hang them on your trees with string. When the traps are covered with flies, brush them off with a wet paper towel, and slather on the same mixture again.
It is also suggested that heavily infested trees be thinned out since whiteflies will proliferate with greater speed in the more humid environment of a densely foliated tree.
For more information about area plants and gardens, go to Joshua Siskin’s website at www.thesmartergardener.com. Send questions and photos to [email protected].
Tip of the Week
If you are looking for an off-the-beaten path ground cover or fence adornment, consider snail vine (Vigna caracalla). It grows up to 25 feet tall but will also trail along the ground. Snail vine grows rapidly and its highly fragrant flowers bloom from March until October. It is not at all thirsty, and it’s hardy down to 20 degrees Fahrenheit. Since snail vine is a legume, it does not require fertilization.
